Autoimmune diseases, type-1 diabetes (T1D) being a classic example, currently afflict around 7% of the population of developed countries. While much progress has been made in deciphering disease mechanisms, many critical issues remain unresolved. A significant hindrance to both mechanistic and therapeutic advances has been the difficulty of dealing with disease entities diagnosed so late in their course, well after the inciting phenomena have played out. Recent impressive advances in the imaging field offer great hope for side-stepping such problems, constituting a powerful impetus for the collaborative Joslin Diabetes Center (JDC)/Massachusetts General Hospital (MGH) imaging program. The program's major objectives are to develop novel imaging strategies, and to exploit them to address critical unresolved issues concerning autoimmune disease in animal models and, ultimately, in human patients. To accomplish these goals efficaciously, the program has been devised around a unique marriage of skills: groups of imaging scientists based at the Center for Molecular Imaging Research at the MGH and groups of immunologists (and more recently (3-cell biologists) at the JDC. These teams collaborate in the context of four projects and one core, whose perspectives include: development of novel imaging probes and modalities;validation in mouse experiments;application to mechanistic issues and establishment of proof-of-principle in murine disease models;and translation to diagnostic or therapeutic problems in the clinic. A palette of imaging target types (microvascular/cellular/molecular/enzymatic) and visualization methods [magnetic resonance imaging (MRI)/positron emission tomography (PET)/confocal and intravital microscopy (IVM)/fluorescence-mediated tomography (FMT), fluorescent-protein tomography (FPT) and mesoscopic fluorescence tomography (FMT) are exploited, and multiple autoimmune diseases (T1 D/arthritis) have been considered. During the past funding cycle, the collaborative imaging program's most significant achievements have been: first, the development of a novel method to non-invasively image pancreatic inflammation in mouse models of T1D, relying on MRI visualization of magnetic nanoparticles (MNP) to read out vascular changes and macrophage activity, a method rapidly translated to a human clinical trial;second, establishment of a new confocal IVM technique to image vascular leak in the joint, resulting in an original concept on the organ-specificity of this disease;third, successful establishment of a novel methodology for non-invasively visualizing fluorescencetagged p-cells in the pancreas of a live mouse (FPT);fourth, development of novel confocal IVM and MFT methods to visualize the pancreas, either exteriorized from a live mouse or as a 3D reconstruction after excision, respectively;and Fifth, substantial improvements in the quality of human pancreas imaging. During the next funding cycle, several of the program's components have evolved to exploit emerging opportunities and to focus specifically on pancreatic islets in the T1D context. Project 1 will continue to develop new imaging probes and modalities, and to perform validation experiments, this cycle focusing on novel in vivo imaging agents with specificity for islet p cells. Both high-throughput screening and candidate approaches will be taken. Project 2 will exploit FPT to establish a novel triple-transgenic mouse system to co-image p-cell mass and p-cell functionality, use the system to address outstanding issues concerning T1D, and continue to exploit MNPMRI to address T1D pathophysiology. Project 3 will employ a combination of MFT and confocal IVM to interrogate the activities of various lymphocyte players in the murine islet lesion. Project 4 will continue and expand the ongoing clinical trial aimed at assessing the value of MNP-MRI as a means of monitoring the unfolding of T1D in humans. The Core will persist in providing service (image acquisition, data analysis) and development (FTP, MFT, clinical microvascular imaging) functions. Some major strengths of this program are that it attacks a critical issue, mobilizes a distinguished group of Pis, is unusually interactive, showed substantial progress over the last funding cycle, and opens a vista of exciting future perspectives. Its uniqueness resides in certain of its resources (imaging probes and modalities, mouse models, patient collections), and in the multiple axes of interaction: imagers/immunologists, physical/chemical/biological inputs, basic/clinical research. The resulting cross-fertilization will almost certainly continue to result in novel solutions to the persisting problems posed by autoimmune disease. PROJECT 1: Novel probes for imaging beta cell mass (Weissleder, R) PROJECT 1 DESCRIPTION (provided by applicant): Beta-cell mass (BCM) and the functional state of islets are critical measures in assessing the magnitude of autoimmune destruction in type 1 diabetes. Progressive loss of BCM is also responsible for the secondary failure of currently available drugs (lack of durability) in type 2 diabetes. Serum tests such as insulin/C-peptide and others do not reliably measure BCM, and currently the only accepted gold standard of measurement is autopsy. It is generally believed that imaging could ultimately be used to a) better understand the history of the islet and the pathophysiology of diabetes, b) enable earlier diagnosis of type 1 diabetes (T1DM), c) allow monitoring of therapeutic efficacy and durability (including islet transplantation), and d) reveal image-able biomarkers useful in the discovery of new therapies. Unfortunately, the necessary tools to quantify BCM are still largely missing. The overall goal of this project is therefore to develop novel in vivo imaging methods and agents with specificity for [unreadable]-cells, in order to non-invasively visualize the target of autoimmune attack in type 1 diabetes. This will be done using powerful library, small-molecule combinatorial and genetic approaches. In close collaboration with the Mathis and Benoist groups, we will validate the most promising agents using accepted gold standards and mouse models. Specifically, we will ask the following questions: 1) what is the in vivo behavior and the putative binding partners of the new affinity ligands? 2) what is the correlation between imaging signal and BCM ? and 3) what are the sources of error in measurements, and how can they be reduced ? The progress to date (new fluorescent mouse models, imaging techniques such as FPT and IVM and new leads from screens to be converted into imaging agents) has been remarkable. The developed agents and strategies will be designed to be clinically translatable, and should add to our previously developed clinical data on imaging islet dysfunction.